The present invention generally relates to an encoder, and more particularly, to an encoder having a plurality of light emitting elements and light receiving elements.
Generally an incremental type encoder is known which is provided with a code plate having a line of slits (i.e. light apertures.) formed regularly therein along a movement direction, and with a plurality of pairs of light emitting elements and light receiving elements disposed along the direction of the slits on both sides of the code plate, so that detection signals having different phases may be obtained from the respective light receiving elements with the by arranging the positions thereof so that the phases become mutually different with respect to the slits.
Also, an absolute type of encoder is also known which includes coded patterns, such as binary coded patterns or the like, formed of a plurality of lines of slits on a code plate, and also, a light emitting element and a light receiving element disposed oppositely to each other on both the sides of the code plate in accordance with the respective coded patterns.
Further, there is disclosed in Japanese Laid-Open Patent Application Tokukaisho No. 61-189415, an encoder of high resolution including the incremental type encoder and the absolute type encoder using code plate 21 having slits 22 and a plurality coded slit patterns 23 formed thereon as shown in FIG. 3.
In the above described incremental type encoder, as shown in FIG. 4, a plurality of light emitting elements 33 are disposed at proper intervals in the direction of the slits on one side of the code plate 31 with many slits 32 being formed therein. A mask 34 with openings 35 formed therein is disposed on the other side of the code plate 31 so as to approximately oppose the respective light emitting elements 33 and to become different in phase to each other with respect to the slits 32, and also, the light receiving element 36 is disposed opposite to the respective openings 35.
In the encoder of the above described absolute type encoder, as shown in FIG. 5, a plurality of light emitting elements 43 are disposed in parallel in accordance with the coded slit patterns 42a, 42b, 42c one side of the code plate 41. A mask 44 with openings 45 corresponding to respectively coded patterns formed therein is disposed on the other side of the code plate 41, and also, a light receiving element 46 is disposed opposite to the each opening 45.
In the incremental type encoder of the above described construction, there are intervals between a pair of light emitting elements 33, 33 and between the light receiving elements 36, 36. As the transmission lights of the slits 32 of the different positions of the code plate 31 are used, error factors such as eccentricity, inclination, working error and so on of the code plate 31 are separately received, with a problem resulting in that stable detection signals are difficult to obtain.
In the absolute type encoder of the above described construction, the intervals of the respective coded patterns 42a, 42b, 42c are required to be made larger, so that crosstalk is not caused with respect to the other light receiving elements 46 through the incidence of the lights which have transmitted through the corresponding coded patterns 42a, 42b, 42c from the respective light emitting element 43 and the openings 45 of the mask 44 only upon the respectively corresponding light receiving element 46 as shown in the break line in FIG. 5. 5, with a problem resulting in that the size of the encoder cannot be made smaller.